Once again, Mother Nature is at the forefront of astrophysical inventions: the ‘camera obscura’ ... inspiring physicists with the principle of how a telescope works. We shall take a look at how such a camera works and how, by slightly modifying it, we can focus the light rays from a distant source onto a single point. We will also show how, using an old record player, a pie plate, a magnifying glass and a little olive oil, you can make a liquid-mirror telescope at your institute, at least 25 cm in diameter. Astronomers and engineers from Liège (Belgium), in association with Indian and Canadian colleagues, have built a much larger one: the 4m International Liquid Mirror Telecope (ILMT). This innovative instrument uses a rotating mirror 4 metres in diameter, coated with a thin film of liquid mercury, to collect and focus the light. A liquid mirror telescope takes advantage of the fact that the surface of a rotating liquid naturally takes on a parabolic shape, which is ideal for focusing light. The reflected light passes through a sophisticated multi-lens optical corrector that produces sharp images over a wide field of view. A large-format electronic camera at focus records the images. The 4-metre International Liquid Mirror Telescope (ILMT) has been installed at the ARIES (Aryabhatta Research Institute for Observational Sciences) site in India's central Himalayas at an altitude of 2,450 m (Devasthal, Uttarakhand). First light was obtained on 29 April 2022 and the telescope is currently recording superb images.
Jean Surdej earned his Physical Sciences degree in 1975, followed by a Ph.D. in Astrophysics in 1979, and an academic habilitation in 1991, all from the University of Liège, Belgium, Faculty of Sciences. He initially pursued his career under the Belgian National Fund for Scientific Research (F.R.S.-FNRS), achieving the title of F.R.S.-FNRS Research Director in 1995. In 2002, he transitioned to an academic path, becoming a Full Professor at the University of Liège in 2007. He has also served as a visiting professor at Adam Mickiewicz University (Poznan, Poland) and as VAJRA Adjunct Faculty at ARIES (Nainital, India). Since October 2017, he has expanded his research, teaching, and training activities internationally, including in Qatar, India, Chile, and Poland. He is actively involved in the 4m ILMT project in ARIES and has regularly visited ARIES since 2012.